This module defines paths, which are collections of concretely
located Trails. Many drawing systems (cairo, svg, ...) have a
similar notion of "path". Note that paths with multiple trails
are necessary for being able to draw e.g. filled objects with
holes in them.

Paths

A path is a (possibly empty) list of LocatedTrails.
Hence, unlike trails, paths are not translationally invariant,
and they form a monoid under superposition (placing one path on
top of another) rather than concatenation.